Thermal current switch



1964 v A. FEHRENBACH ETAL 3, ,9

THERMAL CURRENT SWITCH Filed Nov. '7. 1960 Fig! 2 7 I 8a 5 a 9 /3 6- I l8 W (mam WM Jn venfars Jay: W

Patented Jan. 28, 1954 3,119,912 THERMAL CURRENT SWITCH AlfredFehrenhach, Alexander Diirries, and Heinrich Fraatz, Hameln, Germany,assignors to Licentia Patent-Verwaltungs-Gnu.b..H., Frankfurt am Main,Germany Filed Nov. '7, 1960, Ser. No. 67,742 Claims priority,application Germany Nov. 9, 1959 3 Claims. (Cl. 200-416) The presentinvention relates to a thermal current switch for use as an overloadprotective device in relatively low power equipment, such as householdappliances, oflice machines, small power tools, automotive equipment,and the like.

Equipment of the above type must be provided with suitable protectivemeans which will prevent damage in case of an overload. These means maybe in the form of a thermal current switch which must often beaccommodated in very small spaces, and which must be such that it can bemass-produced at low cost so as not unduly to aiiect the manufacturingcosts of the apparatus with which the switch is to be used. Thus, thereis a definite need for a compact and inexpensive switch which is able toopen an electric circuit in response to temperature rises resulting fromexcess current, and which switch meets the usual requirements insofar asinsulation and reliability are concerned.

l-leretofore known switches have proven to be too complicated and tooexpensive, nor have existing switches been able to meet the rigid spacelimitations which are imposed by the design of modern compact and lightweight electrical appliances. The reason for this is that known switchesincorporate a large number of parts, including a plurality of individualsprings which serve different functions. For instance, in one known typeof switch, one spring is provided for producing the requisite contactpressure between the fixed and movable contacts, another spring isprovided for moving the contacts apart upon overload, and yet anotherspring is provided resetting the switch.

it is, therefore, an object of the present invention to provide athermal current switch which overcomes the above disadvantages.

It is another object of the present invention to provide a thermalcurrent switch which is exceedingly simple in that it incorporates veryfew parts, each readily susceptible to mass-production techniques.

The objects of the present invention also include the provision of aswitch which will open under overload condition even though it isattempted to hold the position manually in closed position.

With the above objects in view, the present invention resides mainly ina thermal current switch which incorporates but a single spring which isrelied on to produce the requisite contact pressure between the fixedand movable contacts, to separate the contacts upon overload condition,and to produce the resetting force for closing the switch.

More particularly, the present invention resides in a thermal currentswitch which comprises a fixed contact, a bimetallic element, anactuator such as a push button carrying a movable contact bridge forconnecting the fixed contact and the bimetallic element, and a singlespring coacting with the contact bridge for producing contact pressurebetween the contact bridge and the fixed contact when the switch isclosed, for moving the contact bridge out of engagement with the fixedcontact upon the occurrence of an overload which produces a deflectionof the bimetallic element, and for producing the resetting force forclosing the switch.

Additional objects and advantages of the present invention will becomeapparent upon consideration of the following description when taken inconjunction with the accompanying drawings, in which:

FIGURE 1 is an elevational view showing the position of the operativecomponents of a switch according to the present invention when theswitch is closed.

FIGURE 2 is a sectional view taken substantially along line 22 of FIGURE1.

FIGURE 3 is a view similar to FIGURE 1, showing the position of theoperative components during an intermediate stage as they move, upon theoccurrence of an overload, from closed to open position.

FIGURE 4 is a view similar to FIGURE 1, showing the position of theoperative components in the open positron.

FIGURE 5 is a View similar to FIGURE 1, showing the position of theoperative components in case the push button is held down at the momentof overload.

Referring now to the drawing and to FIGURES l and 2 thereof inparticular, there is shown a thermal current switch in its normal closedposition. The switch comprises a housing 1, showing in outline form inFIGURE 1 with FEGURE 2 showing this housing as being composed of similarhalves. The housing contains a push button 2 which is mounted forreciprocatory movement relative to the housing 1 between the operativeor depressed position shown in FIGURE 1 and the inoperative or releasedposition shown in FIGURES 3 and 4. The push button 2 carries at itslower end a pivot pin 3 whose extreme ends are slidably received withingrooves 5 formed in the housmg.

The pivot pin 3 serves to connect the push button 2 to a contact bridge4 which is in the form of an elongated conductive element having atapproximately its middle two upwardly bent ears in through which thepivot pin 3 passes, so that the contact bridge 4 is pivotable withrespect to the push button 2; and forms a two-armed lever having arms ofapproximately equal lengths.

The upper surface of the left arm of the contact bridge 4, as viewed inFIGURE 1, carries a movable contact 6 which cooperates with a fixedcontact '7 carried by a terminal strip 14 mounted in the housing 1,whereas the upper surface portion at the end of the right arm is engagedby a detent carried at the free end of a bimetallic strip 8 whose lowerend is connected to the housing 1 as well as to a terminal strip 15.

The upper end of a coil spring 9 surrounds a projection ll located onthe underside of the contact bridge 4 at a point intermediate thepivotal connection between the bridge and the push button, i.e., themiddle of the contact bridge, and the surface portion engaged by thedetent 8a. The lower end of the spring 9 is received in a well or recesslltl formed in the housing 1. This spring, which, as shown, is looselyinserted into the switch, is the only spring element that is needed. aswill be explained below.

The switch further comprises two abutments l2 and 13, the purpose ofwhich will be explained below. Also, the housing l is formed withopenings 16 and 17 through which may pass mounting elements, so that theswitch may readily be mounted on the appliance with which it is used bythreading it onto suitable mounting rods.

The operation of the switch will now be explained with reference toFIGURES l, 3, 4 and 5.

FIGURE 1 shows the switch in closed position, the contacts 6 and '7being held in engagement with each other with the necessary contactpressure and the right end of the contact bridge being pressed againstthe detent 8a of the bimetal strip 8 by the action of the spring 9which, in this position, is in compressed state. Thus, an electriccurrent may flow from the terminal strip 14-, through the contacts 7, 6,the contact bridge 4, the detent 8a, the bimetal strip 8, and theterminal strip 15. The bimetallic strip d, of course, is shown in theposition which it occupies when the current flowing through the switchis not greater than the maximum permissible current.

Should now the current through the switch exceed the permissiblemaximum, the temperature of the bimetallic strip 3 will increase to apoint where the strip will deflect such as to move the detent 3a out ofengagement with the contact bridge 4. As a result, the spring 9 willpivot the right arm of the contact bridge 4- upwardly, thereby urgingthe push button upwardly towards its inoperative position. During thefirst stage of the switch opening movement, shown in FIGURE 3, thecontacts 6, 7 will remain in engagement with each other, i.e., thecontact bridge 4 pivots at first about the point of engagement betweenthe two contacts 6 and 7. This engagement will not be broken until theleft arm of the contact bridge 4 strikes the abutment 12. The kineticenergy of the contact bridge, at the instant it reaches against theabutment 12, will cause the bridge to be subjected to an abrupt strikingeffect which increases the speed with which the contacts 6 and 7 areseparated, i.e., the contacts will be opened in a sudden or jerkymanner. This means that the contacts 6 and 7 will be separated from eachother more quickly than if the abutment 12 were not provided.

After striking the abutment 12, the contact bridge 4 continues itsmovement until it engages the lower abutment 13, as shown in FIGURE 4.This is the position of the component parts after the switch-openingmovement has been completed.

After the bimetallic strip 8 has cooled, the switch may be closed bydepressing the push button 2. This will move the pivot pin 2%downwardly, so that the contact bridge 4 will at first remain inengagement with and pivot about the abutment 1.3 inasmuch as the spring9 tends to rotate the contact bridge 4 in counterclockwise direction.The depressing of the push button will compress the spring 9 until theright arm engages the detent Sn, and the contacts 6 and 7 may then bebrought into engagement with each other by releasing the push button 2;this will cause the contact bridge 4 to pivot about the detent 8a, underthe influence or" the spring 9, in clockwise direction. The switch isthus reset into closed position and is ready to function again in caseof overload.

it will be seen from the above that the single spring 9 serves athree-fold function, namely, the spring (1) pro- 'duces the contactpressure between the movable contact *6 of the contact bridge 4 and thefixed contact 7 when the switch is in closed position, (2) moves thecontact bridge 4 out of engagement with the fixed contact 7 upon theoccurrence of an overload which produces a deflection of the bimetallicstrip 8, and (3) produces the resetting force for closing the switch.Inherent in (2) is, of course, that the spring 9 also acts to move thepush button 2 from its operative position to its inoperative position.

FIGURE shows that if it were attempted to hold :the switch closedmanually at the instant an overload current flows through the switch,the switch would still open. This is so because upon deflection of thebimetallic strip 8, the right arm of the contact bridge 4 will be movedupwardly under the influence of the spring 9, thereby separating thecontacts 6 and 7. Of course, the contact bridge would then not firstpivot about the point of engagement between the contacts 6 and 7, butwould immediately pivot about the pivot pin 3. The contact bridge 4would ultimately assume the position illustrated in FIGURE 5 wherein theright arm is shown as engaging the abutment 13. Upon release .of thepush button 2, the operative components of the switch would assume theposition shown in FIGURE 4.

FIGURE 5 also shows that if it is attempted to reclose the switch beforethe bimetallic strip 8 has cooled sufficiently to allow the detent 8a toengage the right arm of the contact bridge 4, the contact bridge 4 wouldsimply pivot about abutment 113, i.e., if the push button is depressedwhile the parts are as shown in FIGURE 4, they will simply assume theposition shown in FIGURE 5 and no resetting of the switch is possible.Of course, once the bimetallic strip 8 has cooled sulficiently to returnto the condition shown in FIGURE 1, the above-described resettingoperation could be carried out.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

We claim:

1. A thermal current switch comprising, in combination: a housing; afixed contact carried by said housing; a bimetallic strip having one endthereof connected to said housing, said bimetallic strip having at itsother end a detent; a push button mounted in said housing forreciprocatory movement relative thereto and carrying a pivot pin havingends slidably received in grooves of said housing; a contact bridgepivotally connected to said pivot pin, said pivot pin being connected tosaid contact bridge at a point intermediate its ends so that saidcontact bridge forms a two-armed lever, said contact bridge carrying onone arm thereof a movable contact cooperating with said fixed contact,the other arm of said contact bridge being engageable by said detent ofsaid bimetallic strip; and a single spring coacting with said contactbridge for producing contact pressure between said fixed and movablecontacts when said switch is in closed position, for moving saidcontacts out of engagement with each other upon the occurrence of anoverload which produces a deflection of said bimetallic strip resultingin a disengagement of said detent from said other arm of said contactbridge, and for producing the resetting force for closing the switch,said spring being loosely inserted in said housing, one end of saidspring being received within a recess in said housing and the other endof said spring being operatively connected to said other arm of saidcontact bridge to act on a point thereof which is between the point atwhich said pivot pin is connected to said contact bridge and the pointat which said detent of said bimetallic strip engages said other arm ofsaid contact bridge.

2. A thermal current switch as defined in claim 1 wherein the operativeconnection between said contact bridge and said spring is established bya projection carried by said contact bridge, said projection being inengagement with said other end of said spring.

3. A thermal current switch as defined in claim 1, further comprising anabutment for increasing the speed with which said contacts are separatedunder the influence of said single spring, said abutment being locatedto be engaged by said one arm of said contact bridge when the latter ismoved under the influence of said spring, thereby allowing pivoting ofsaid contact bridge, still under the influence of said spring, aboutsaid abutment to separate said movable contact from said fixed contact.

References Cited in the file of this patent UNITED STATES PATENTS2,335,082 Platz Nov. 23, 1943 2,409,917 Von Hoorn Oct. 22, 19462,418,537 Wood Apr. 8, 1947 2,492,382 lngwersen Dec. 27, 1949 2,741,681Allard Apr. 10, 1956 2,952,757 Ellenberger Sept. 13, 1960

1. A THERMAL CURRENT SWITCH COMPRISING, IN COMBINATION: A HOUSING; AFIXED CONTACT CARRIED BY SAID HOUSING; A BIMETALLIC STRIP HAVING ONE ENDTHEREOF CONNECTED TO SAID HOUSING, SAID BIMETALLIC STRIP HAVING AT ITSOTHER END A DETENT; A PUSH BUTTON MOUNTED IN SAID HOUSING FORRECIPROCATORY MOVEMENT RELATIVE THERETO AND CARRYING A PIVOT PIN HAVINGENDS SLIDABLY RECEIVED IN GROOVES OF SAID HOUSING; A CONTACT BRIDGEPIVOTALLY CONNECTED TO SAID PIVOT PIN, SAID PIVOT PIN BEING CONNECTED TOSAID CONTACT BRIDGE AT A POINT INTERMEDIATE ITS ENDS SO THAT SAIDCONTACT BRIDGE FORMS A TWO-ARMED LEVER, SAID CONTACT BRIDGE CARRYING ONONE ARM THEREOF A MOVABLE CONTACT COOPERATING WITH SAID FIXED CONTACT,THE OTHER ARM OF SAID CONTACT BRIDGE BEING ENGAGEABLE BY SAID DETENT OFSAID BIMETALLIC STRIP; AND A SINGLE SPRING COACTING WITH SAID CONTACTBRIDGE FOR PRODUCING CONTACT PRESSURE BETWEEN SAID FIXED AND MOVABLECONTACTS WHEN SAID SWITCH IS IN CLOSED POSITION, FOR MOVING SAIDCONTACTS OUT OF ENGAGEMENT WITH EACH OTHER UPON THE OCCURRENCE OF ANOVERLOAD WHICH PRODUCES A DEFLECTION OF SAID BIMETALLIC STRIP RESULTINGIN A DISENGAGEMENT OF SAID DETENT FROM SAID OTHER ARM OF SAID CONTACTBRIDGE, AND FOR PRODUCING THE RESETTING FORCE FOR CLOSING THE SWITCH,SAID SPRING BEING LOOSELY INSERTED IN SAID HOUSING, ONE END OF SAIDSPRING BEING RECEIVED WITHIN A RECESS IN SAID HOUSING AND THE OTHER ENDOF SAID SPRING BEING OPERATIVELY CONNECTED TO SAID OTHER ARM OF SAIDCONTACT BRIDGE TO ACT ON A POINT THEREOF WHICH IS BETWEEN THE POINT ATWHICH SAID PIVOT PIN IS CONNECTED TO SAID CONTACT BRIDGE AND THE POINTAT WHICH SAID DETENT OF SAID BIMETALLIC STRIP ENGAGES SAID OTHER ARM OFSAID CONTACT BRIDGE.